1. Field of the Invention
The invention relates to novel drill-hole treatment agents which are fluid under normal conditions and have been composed by using an oil phase in combination. Referring to a characteristic example for treating agents of this kind, the invention is described hereinbelow by way of drilling fluids and drilling muds formed therewith. However, the field of application of the modification according to the invention of auxiliary liquids of the kind involved here is not limited thereto, while it also includes in particular the areas of spotting fluids, spacers, auxiliary liquids for workover and stimulation and for fracturing.
Concerned by the invention are auxiliary liquids of the kind mentioned which are oil-based, i.e. which work using a continuous oil phase, as well as auxiliary agents wherein the oil phase has been emulsified in an especially aqueous continuous phase. Here, drilling fluids and drilling muds formed therewith are characteristic examples of the various possibilities.
There have been known, on the one hand, water-based drilling fluids having a content of from about 1 to 50% of emulsified oil phase--besides the other conventional auxiliary materials of such a drilling fluid--which are designated as emulsion fluids. On the other hand, there are being used to a wide extent in practice oil-based fluid systems wherein the oil constitutes the fluid phase or at least the predominant portion of the fluid phase. Here the so-called inverted drilling muds are of particular importance which, based on W/O emulsions, contain a dispersed aqueous phase in the continuous phase. The content of the dispersed aqueous phase usually is within the range of from about 5 to 50% by weight. The invention equally relates to both of the fields as mentioned here of the oil-based sweeping systems and of the water-based sweeping systems based on emulsions.
The use of the new fluid drilling-hole treatment agents is of particular importance for the exploitation of crude oil and natural gas, especially in the marine sector, while it is not limited thereto. The new systems may find general use in terrestrial drilling, for example in geothermal drilling, water drilling, in carrying out geo-scientific drilling and in drilling in the field of mining.
2. Prior art
Liquid sweeping systems for rock-drilling to bring-up the removed drill cuttings have been known to restrictedly thickened fluid systems which may be assigned to one of the three following classes:
Merely aqueous drilling fluids, oil-based drilling fluid systems which, as a rule, are used as so-called inverted emulsion drilling muds, and the water-based O/W emulsions which contain a heterogeneous finely dispersed oil phase in a continuous aqueous phase.
Drilling fluids having a continuous oil base in general are composed as a three-phase system: Oil, water and finely divided solids. Therein the aqueous phase has been heterogeneously distributed in a finely dispersed state in the continuous oil phase. A multiplicity of additives is provided, more specifically emulsifiers, weighting agents, fluid-loss additives, alkali reserve, viscosity modifiers and the like. As to details, reference is made, for example, to the publications P. A. Boyd et al., "New Base Oil Used in Low-Toxicity Oil Muds", Journal of Petroleum Technology 1985, 137 to 152, and R. B. Bennett, "New Drilling Fluid Technology--Mineral Oil Mud", Journal of Petroleum Technology 1984, 975 to 981, as well as the literature quoted therein.
Drilling fluids comprised of water-based O/W emulsion systems with view to their utility properties occupy an intermediate position between the neat aqueous systems and the oil-based inverted fluids. Extensive substantial information is found in the pertinent technical literature; reference may be made, for example, to G. R. Gray and H. C. H. Darley, "Composition and Properties of Oil Well Drilling Fluids", 4th Edition, 1980/81, Gulf Publishing Co., Houston, and the voluminous substantial and patent literature quoted therein, and to the reference book "Applied Drilling Engineering", Adam T. Bourgoyne Jr. et al., First Printing Society of Petroleum Engineers, Richardson, Tex. (U.S.A.).
Today the oil phases of drilling fluids of the type described here and comparably composed other drill-hole treatment agents in practice are almost exclusively formed by mineral oil fractions. This involves a considerable environmental pollution, if, for example, the drilling muds directly or via the drilled rock will infiltrate the environment. Mineral oils are only difficult to decompose and are virtually not anerobically degradable at all and, thus, to be rated as long-term pollutants.
More recently there have been made some proposals to reduce the above problems. Thus, the U.S. Pat. Nos. 4,374,737 and 4,481,121 describe oil-based inverted drilling fluids wherein so-called non-polluting oils are reported to have been used. As the non-polluting oils there have been mentioned side by side and equivalently mineral oil fractions which are free of aromatics and ester oil of vegetable and animal origin. Said ester oils are triglycerides of natural fatty acids which are known to have a high environmental compatibility and under ecological considerations are clearly superior to hydrocarbon fractions.
Applicant, in a greater number of older publications, describes proposals substituting the mineral oil fractions with ecologically compatible readily degradable oil phases. Thereby, four different types of substituting oils have been presented which may also be used as mixtures. They include selected oleophilic monocarboxylic acid esters, at least largely waterinsoluble alcohols which are fluid under the operation conditions, corresponding ethers and selected carbonic acid esters. In summary, reference is made here to the older applications U.S. Ser. No. 07/759,097, now U.S. Pat. No. 5,232,910; U.S. Ser. No. 07/825,431, now U.S. Pat. No. 5,252,554; U.S. Ser. No. 07/752,694, now abandoned; U.S. Ser. No. 07/752,692, now abandoned; U.S. Ser. No. 07/825,436, now U.S. Pat. No. 5,254,531; U.S. Ser. No. 07/478,189, now U.S. Pat. No. 5,106,516; U.S. Ser. No. 07/768,937, now abandoned; and U.S. Ser. No. 07/768,419, now abandoned. All of the older applications mentioned here relate to the field of oil-based drilling fluid systems, especially of the W/O inverted type. Water-based emulsion fluids using oil phases of an increased degradability have been described in the older applications, U.S. Ser. No. 07/776,003, now abandoned and U.S. Ser. No. 07/773,631, now U.S. Pat. No. 5,194,422 and U.S. Ser. No. 07/777,376, now abandoned and the already mentioned application Ser. No. 07/955,738, filed Dec. 7, 1992, now pending.